The present invention relates generally to electromagnetic switching devices, particularly to circuit breakers of the type having a stationary magnetic core and a movable armature which is supported for movement above the core in a guiding member.
In electrical switching devices of this kind it is very important that the stroke of the armature, that is the spatial interval which the armature travels from its starting position on actuation of the switching device up to its abutment on the magnetic core, be adjusted accurately. In practice, this requirement cannot be accurately fulfilled, and the resulting inaccuracy has been tolerated. There are different reasons for this inaccuracy. For example, in manufacturing of the switching devices, certain production tolerances which affect the actual stroke of the armature, are unavoidable. In addition, in operation of the switching device certain changes in the stroke of the armature occur after a certain time period, either due to wear or burning of the contact pieces present in the switching system. As a result, an interfering buzzing of the magnetic drive will occur.